1. Filed of the Invention
The present invention generally relates to a heating structure suitable for applying heat to a joint used for providing a connection between piping or to a joint used for providing a connection between a pipe and an associated device.
2. Description of the Related Art
In recent years, as an exhaust emission purifying apparatus for purifying nitrogen oxides (NOx) contained in the exhaust gas of a diesel engine, there has been proposed a selective catalytic reduction (SCR) apparatus using a liquid reducing agent, such as the urea water or the like. In order to enhance the purifying efficiency of a nitrogen oxide reduction catalytic converter disposed in an exhaust passage, this apparatus adopts a configuration in which the liquid reducing agent is added into the exhaust gas during passing through a certain section of the exhaust passage that is arranged on the upstream side of the nitrogen oxide reduction catalytic converter,
In such an exhaust emission purifying apparatus using the liquid reducing agent, in the case where the urea water is used as the liquid reducing agent thereof, countermeasures against freezing of the liquid reducing agent must be made on piping through which the urea water is flown. This is because the urea water is frozen at a temperature below zero but at a relatively high predetermined temperature which might be met in rather cold weather regions.
Structures of keeping the piping warm by a heat-insulating material or heating the piping by a heater are widely adopted in fields of water supply lines, plant facilities and the like. In these known structures, a joint (including a connector and a flange) portion for connecting the pipe to the other side device or for connecting between different pipes is covered by the heat-insulating material or is wounded by a heater, separately from piping body, as disclosed in FIG. 5 and FIG. 6 of Japanese Unexamined Patent Publication No. 1992(H04)-102793.
However, the above conventional art relies on a technique on the premise of manual works, and therefore, involves an amount of efforts, and further, the stabilization of assembly quality is hard to be achieved due to individual differences in workers. Further, the entire joint portion is covered separately from the piping portion to thereby need much space, and therefore, such a conventional technology is not suitable for a pipe layout installed in an exhaust emission purifying apparatus having only a narrow disposing space.
On the other hand, in blow-by gas piping, there is also an example adopting, as a joint, a connector with a built-in heater. However, such a connector, that is, the joint with a built-in heater, is a specific component peculiarly designed for a specified engine, and accordingly, there is a problem in that the cost incurred for the molds for manufacturing the component must increase especially in the case of a small amount of production.